Self-luminous devices due to their fast response speeds, high color gamut, high contrast, large display angles and other advantages, are gradually applied to display products.
At present, the self-luminous display mainly includes: a plasma display panel, an electrophoresis display, a field emission display, a surface-conduction electron-emitter display, an organic light-emitting diode (OLED) display and the like.
FIG. 1 is a driving circuit of OLED pixel units. As shown in FIG. 1, the driving circuit of OLED pixel units includes two transistors and a capacitor. One of the transistors is a switch T1 controlled by a scanning signal Vscan outputted by a row driving circuit, for the purpose of controlling an input of a data signal Vdata on a data line, and the other transistor is the driving transistor T2, which is conductive as being driven by the driving voltage Vdata to control the OLED to emit light. Cs is a storage capacitor which is configured to maintain the driving voltage applied to the driving transistor T2 during a non-scanning period. The OLED can emit light due to the driving of the current generated by the driving transistor is in a saturated state. When the same grayscale voltage is inputted, different driving threshold voltages of the pixel units may generate different driving currents, thereby resulting in inconsistencies of the driving currents. Since it is difficult to ensure the uniformity of the threshold voltage Vth of the pixel unit, therefore, the uniformity of the driving current of the self-emitting display is poor when it is driven at low voltages, that is, at low grayscales. At the same time, since the Vth also drifts along with the use of the pixel units, the brightness uniformity of the self-luminous display deteriorates with the aging of the OLED pixel units.
At present, in order to improve the problem that the low grayscale uniformity is getting worse due to the aging of the self-luminous display, the driving circuit design of the self-luminous display includes two parts: a normal driving circuit and a compensating circuit, where the normal driving circuit ensures that a video signal content is normally displayed, and the compensating circuit is configured to detect the condition about the aging of the display, and provide compensations in the driving signal accordingly. In the compensating circuit, a current detection line is shared among each column of pixels to detect the driving current of the pixels. A current comparing circuit is provided at the end of the current detecting line. The Vth drift data ΔVth of the self-luminous display is determined by comparing the current before and after continuous operation of the self-luminous display according to the relationship between the current and the voltage of the self-luminous display:Ids=β(Vdata−Vth)α
Where β and α are proportional constants, Ids is the driving current of the self-luminous device, Vth is the threshold voltage of the self-luminous device, and Vdata is the actual driving voltage. From the above equation, it can be seen that when Vth is shifted and the Vth data is gradually increased, Ids will gradually decrease under the same Vdata signal voltage. The determined ΔVth is added to the actual Vdata signal voltage for compensation, in order to overcome defects such as the non-uniformity of the low grayscales caused by the Vth drifting.
However, the inventor has found that although the grayscale compensating method described above can improve the brightness performance of the self-luminous display at high grayscales, however, the uniformity of the self-luminous display at low grayscales has not been effectively improved.